1. Field of the Invention
The present invention relates to a marine propulsion machine including a vertical drive shaft driven for rotation by an engine, an output gear mechanism to which the power of the drive shaft is transmitted, a propeller shaft driven for rotation by power transmitted thereto through the output gear mechanism, and a water pump driven by the drive shaft.
2. Description of the Related Art
Marine propulsion machines are known which are provided with a drive shaft including a first drive shaft interlocked with an engine, and a second drive shaft interlocked with the first drive shaft by an intermediate gear mechanism (see, for example, Japanese Patent Application Publication Nos. 5-52107, 63-97489 and 3-21589. Marine propulsion machines are also known in which a gear case is provided with water intakes formed in parts thereof on the front side of drive shafts and a water pump driven by the drive shaft sucks water through the water intakes (see, for example, Japanese Patent Application Publication Nos. 3-21589 and 5-270490).
The gear case provided with the water intakes on the front side of the drive shafts is provided with a shift rod for changing ship propelling directions on the front side of the drive shafts. In some cases it is difficult to secure a space sufficient for forming the water intakes when members are disposed and passages are formed on the front side of the drive shafts.
For example, if the water intakes are formed in a big vertical dimension to form the water takes in a predetermined area when the longitudinal dimension of the water intakes is limited to avoid positional coincidence between the shift rod and the water intakes, the upper ends of the water intakes are at a high vertical position nearly corresponding to the surface level of the water and air is liable to be sucked in together with water.
In a marine propulsion machine having a gear case having a gearing holding portion holding an output gear mechanism and provided with water intakes, a suction passage extending between the water intakes and a water pump is long and causes a large pressure loss. Therefore, the water intakes need to be formed in a large area, and the size of the gearing holding portion needs to be increased or the capacity of the water pump needs to be increased accordingly. Thus power loss caused by a drive shaft driving the large-capacity water pump increases.
The drive shaft connected to the water pump is required to be corrosion-resistant or rustproof and hence the drive shaft is made of a highly corrosion-resistant material, such as a stainless steel. Such a highly corrosion-resistant material is expensive. Therefore, increase in the length of the drive shaft made of a highly corrosion-resistant material increases the cost of the marine propulsion machine.